Electronics > Beginners
Setting a scope scale
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David Hess:

--- Quote from: JS on August 09, 2018, 02:15:40 am ---The nice part of the external variable reference and a differential probe is that, in some special cases, you could use some AC for your reference, in sync with the signal composed of a similar AC and some smaller amplitude signal on top. I wander how useful it might be but I guess some cases would appreciate this, like measuring distortion in audio signals, where you generate the original signal and then some other stuff appears on top of it.
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AC bridge measurement is a good example of what you are suggesting.

I doubt it would be useful for audio distortion measurement because limited common mode rejection limits precision.
JS:



--- Quote from: David Hess on August 09, 2018, 03:28:28 am ---AC bridge measurement is a good example of what you are suggesting.

I doubt it would be useful for audio distortion measurement because limited common mode rejection limits precision.

--- End quote ---
I don't think THD measurement would work, but characterization of the distortion, like clipping recovery time or windup effcts, or more extreme distortion situations. 0.001% is out of the reach of an oscilloscope for sure, but the shape of a 2%THD might if you can get rid of the fundamental.


JS

David Hess:

--- Quote from: JS on August 09, 2018, 04:01:01 am ---I don't think THD measurement would work, but characterization of the distortion, like clipping recovery time or windup effcts, or more extreme distortion situations. 0.001% is out of the reach of an oscilloscope for sure, but the shape of a 2%THD might if you can get rid of the fundamental.
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Assuming a perfect 8 bit DSO, distortion measurements down to 0.3% could be possible.  In practice, at least 1% should be feasible with the FFT function on a real instrument.

JS:

--- Quote from: David Hess on August 09, 2018, 07:11:40 pm ---
--- Quote from: JS on August 09, 2018, 04:01:01 am ---I don't think THD measurement would work, but characterization of the distortion, like clipping recovery time or windup effcts, or more extreme distortion situations. 0.001% is out of the reach of an oscilloscope for sure, but the shape of a 2%THD might if you can get rid of the fundamental.
--- End quote ---

Assuming a perfect 8 bit DSO, distortion measurements down to 0.3% could be possible.  In practice, at least 1% should be feasible with the FFT function on a real instrument.

--- End quote ---

You could be able to say it has about 1%THD but you are a long way to say something useful about that distortion, like what to do in order to minimize it, or make it less audible, like the recovery time or windup I said.

JS
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